Stomata play a key role in the control of plant water relations and photosynthesis. A rapid non-destructive method to study the stomatal behaviour in aerial parts of plants is important for researchers in plant sciences and agricultural fields. Stomata close in response to drought stress. Stomatal closure causes lower availability of CO2 inside the leaf and thus a decrease in the rate of carboxylation. Thus, a measurement of relative quantum yied for electron transport by photosystem II (ΦPSII) under a non-photorespiratory condition may be used to detect the closure of stomata. In this research we aimed to study the relationship between ΦPSII and stomatal closing behaviour in Tradescantiavirginiana under water stress and rehydration using a chlorophyll fluorescence imaging system.